Fluorometholone, clobetasone butyrate and clobetasol propionate used in the present invention are synthetic adrenocortical hormones each exhibiting a strong anti-inflammatory action and, in particular, fluorometholone and clobetasone butyrate are drugs effective for treating inflammatory diseases at external-ocular and anterior-ocular sites. However, these drugs are hardly soluble in water and therefore, it is impossible to dispense these drugs like the usual aqueous eye drops. For this reason, fluorometholone and clobetasone butyrate have been used in ophthalmology in the form of an aqueous suspension prepared by pulverizing crystals of each drug into fine particles and dispersing and suspending the particles in an appropriate amount in an aqueous solution for eye drops, but these aqueous suspensions suffer from problems such that they are bad in feeling when they are applied to the eyes and that the fine particles thereof precipitate and solidify at the bottom of the container thereof, as a result, they are never redispersed uniformly even if the suspension is vigorously shaken. Moreover, solubility of crystal particles of fluorometholone and clobetasone butyrate in the tear fluid is low and therefore, the bioavailability thereof is also low.
In general, drugs hardly soluble in water have been solubilized therein by the use of various kinds of surfactants or other additives having effects similar to those of the surfactants. However, such additives used in commercially available eye drops as medical additives have been limited to those having relatively weak solubilization ability from the viewpoint of safety. Therefore, it is difficult to solubilize drugs hardly soluble in water such as fluorometholone, clobetasone butyrate and clobetasol propionate in an amount effective for preparing pharmaceutical preparations thereof. Under such circumstances, there has been proposed a method in which fluorometholone is included in dimethyl-.beta.-cyclodextrin to thus enhance the solubility thereof in water [Japanese Un-Examined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Sho 59-130900] and a method in which clobetasone butyrate is included in heptakis(2,6-di-O-methyl)-.beta.-cyclodextrin to thus enhance the solubility thereof in water(J. P. KOKAI No. Sho 61-129115), but such methods have not yet been put into practical use.
On the other hand, there have been disclosed O/W emulsion compositions each of which comprises a drug, an oil, a phospholipid and a surfactant (J. P. KOKAI No. Hei 5-186333 and WO 94/05298) as prior arts concerning vehicles for instilled drugs hardly soluble in water in the eyes.